WASHINGTON — President Barack Obama’s top health official apologized on Wednesday for the botched rollout of the government’s healthcare website, acknowledging it was a “debacle,” while also blaming insurers for canceling coverage for hundreds of thousands of people.

Health and Human Services Secretary Kathleen Sebelius, testifying at a congressional hearing on the troubled website at the heart of Obama’s healthcare overhaul, vowed to win back the confidence of millions of disappointed Americans.

“Hold me accountable for the debacle. I’m responsible,” Sebelius said in response to questions from Marsha Blackburn, the Republican U.S. Representative of Tennessee, about who was responsible for problems that have prevented people from signing up for healthcare insurance plans.

Technical glitches have dogged Healthcare.gov since its launch on October 1, preventing many people from signing up for insurance plans. But critics of Obamacare have seized on the hundreds of thousands of Americans due to lose their current plans because they fail to include essential benefits required by the law and are asking whether Obama misrepresented the law.

Sebelius, the cabinet official spearheading the implementation of the 2010 Affordable Care Act, known as Obamacare, drew intense criticism from Republicans including Fred Upton, chairman of the House Energy and Commerce Committee. Upton accused Obama of breaking a 2009 promise that people with insurance could keep their current plans.

“They are now receiving termination notices, and for those who lose the coverage they like, they may also be losing faith in their government,” the Michigan Republican said.

Sebelius defended the administration by describing hundreds of thousands who have received cancellation notices as the victims of a market long known for discriminating against the sick, cancelling policies and selling inadequate insurance.

“The individual market … anywhere in the country has never had consumer protections. People are on their own. They can be locked out, priced out, dumped out,” by insurers, Sebelius said.

Sebelius said Obama had not broken his promise because plans that have existed since the law was signed have had the option of remaining unchanged.

Democrats on the committee rallied to the administration’s position by pointing out that insurance policies being canceled would be replaced by better plans that meet higher standards under Obamacare, many of them at lower costs.

“I would urge my colleagues to stop hyperventilating,” said Representative Henry Waxman of California, the committee’s top Democrat.

Sebelius has become a political punching bag for Republicans who have repeatedly called on her to resign over the flawed rollout of the website. The White House continues to support her.

“I am as frustrated and angry as anyone with the flawed launch of Healthcare.gov,” Sebelius testified. “So let me say directly to these Americans: You deserve better. I apologize.

“I’m accountable to you for fixing these problems. And I’m committed to earning your confidence back by fixing the site.”

The hearing was convened to discuss problems with Healthcare.gov, the federal government’s portal to online health insurance marketplaces for millions of uninsured Americans in 36 states. The site was crippled by technical glitches at its launch and continues to be plagued by issues including outages.

The administration has set itself a late-November deadline for resolving the issues at Healthcare.gov. Experts say that leaves little time for additional error. Failure to enable uninsured people to sign up for coverage beginning January 1, when the law comes into full force, could jeopardize Obama’s goal of enrolling 7 million people through online marketplaces in 2014.